ABSTRACT: Crustal Types, Distribution of Salt and the Early Evolution of the Gulf of Mexico Basin

Richard T. Buffler

A new contour map on the top of basement shows the overall configuration of the entire Gulf of Mexico basin. Basement, as used here, is all rocks lying below (older than) the extensive Middle Jurassic (Callovian?) premarine evaporites (Louann Salt, etc.) plus the Late Jurassic oceanic crust in the deep part of the basin. The contour map combined with all other available geophysical data has been used to subdivide the gulf basin into four crustal types: continental, thick transitional, thin transitional, and oceanic crust. The broad region of transitional crust and the basic architecture of the basin shown by the map is believed to have formed mainly during a separate Middle Jurassic period of widespread attenuation of the entire gulf region. The area of thick transitional crust around the periphery of the northern gulf is characterized by broad basement highs and lows with wave lengths of 200-300 km. These features controlled the general distribution and thickness of salt and the overlying Jurassic through Lower Cretaceous rocks. In the area of thin transitional crust, Mesozoic basins tend to be assymetrical and generally trend more parallel to the overall basin. The boundary between thin transitional crust and oceanic crust is characterized by various salt-related features. For example, the northwest and north-central boundaries are defined by two northeast-trending salt-cored foldbelts, the Perdido and Mississippi fan foldbelts, respectively. The offset between the two foldbelts may represent a major transform boundary related to the northwest opening o the gulf basin. All these data put important constraints on models for early gulf evolution.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990